1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device for improving a color viewing angle.
2. Discussion of the Related Art
Generally, light emitting devices are categorized into organic light emitting display devices that have an emission layer formed of an organic material and inorganic light emitting display devices that have an emission layer formed of an inorganic material. In such light emitting devices, the organic light emitting display devices are self-emitting devices in which, an electron injected from a cathode and a hole injected from an anode are combined with each other in an organic emission layer to form an exiton, and the exiton releases energy to emit light. The organic light emitting display devices are driven with low power, self-emit light, realize a natural color, and have a wide viewing angle, high resolution, and a fast response time.
Recently, as organic light emitting display devices emitting white light are developed, the organic light emitting display devices are widely applied to various fields such as backlight, lighting, etc., and thus are recognized as a most important type of display device.
In types where the organic light emitting display devices realize white, there are a single-photon emission type, a multi-photon emission type, a color conversion type, and a stack type. Among such types, the multi-photon emission type in which light is emitted from a multi-layer and white is realized by vertical combination of colors is widely used.
Specifically, as shown in FIG. 1, organic light emitting display devices based on the multi-photon emission type having a 2-stack structure externally emit electroluminescent (EL) spectrum light having two peaks
However, the above-described organic light emitting display devices of the related art have the following limitations.
FIG. 1 is a view showing an EL spectrum and an emittance spectrum that are changed according to a viewing angle, and a photoluminescence (PL) spectrum that is hardly changed according to the viewing angle, in a related art organic light emitting display device. FIG. 2 is a view showing that the intensities of blue light B and yellowish green light YG are reduced according to a viewing angle, in the related art organic light emitting display device of FIG. 1.
As seen in FIG. 1, an EL spectrum 30 in which final light emitted from the related art organic light emitting display device has been spectrum-analyzed is expressed as the multiplication of a PL spectrum 10 (which is a spectrum of light emitted from an emission layer) and an emittance spectrum 20 that is changed according to the optical characteristic and thickness of a layer configuring an organic emission layer.
As seen in the PL spectrum 10, the related art organic light emitting display device includes an emission layer that emits (B PL) the peak wavelength of blue, and an emission layer that emits (YG PL) the peak wavelength of yellowish green, thereby emitting white light. However, since an amount of reduced intensity of blue light differs from an amount of reduced intensity of yellowish green light, the white light is reduced in color viewing angle characteristic.
That is, as seen in the EL spectrum 30 and FIG. 2, as a viewing angle increases from 0 degrees to 60 degrees, the intensity of blue light is rapidly reduced, but the intensity of yellowish green is relatively slowly reduced. For this reason, in a difference between white light realized in the front (a viewing angle of 0 degrees) and white light realized in a side surface, color shift increases (the reduction in color viewing angle characteristic) progressively closer to a side surface (the increase in a viewing angle).
Moreover, as seen in the EL spectrum 30, it can be seen that the intensity of red (R) light is lower than those of blue light and green light. Therefore, the current density of a red sub-pixel increases for realizing sufficient luminance, and thus, a Voled voltage increases and the light emission efficiency of a panel decreases.